If you're not already following Kill Six Billion Demons, consider starting. But anyway: Gog-Agog is a demiurge, one of seven evil demigods who run the K6BD multiverse. She's basically a Pathfinder Worm That Walks -- a wriggling mass of worms animated by a single powerful colonial intelligence -- and she runs the multiverse's entertainment industry.

Here are some fun things about Gog-Agog that could be adopted to Pathfinder:

1) She seems to have the power to infect people with her worms. The host is then under her complete control; she can see/sense whatever it sees or senses. Worse yet, at will she can move her consciousness into the host. The unfortunate host is immediately devoured by an frantically growing mass of worms, with Gog-Agog bursting explosively out of the host's body in a single round. Think the Alien chestburster, only full-body. Needless to say, this kills the host very dead. The details of this horrific power are unclear; there doesn't seem to be any range limitation or anything. Presumably the host has to be willing or helpless to be infected. (Yeah, "willing" seems unlikely, but OTOH it's the entertainment industry, so who knows.)

2) Gog-Agog can appear completely human (or as any other small, medium or large-sized humanoid) to casual examination Close examination will show that she's really a mass of differently colored worms holding humanoid form, but you have to get within 10' and be paying attention. Gog-Agog regularly tinkers with new forms, usually young and attractive. A complication: none of these forms are stable. After a few minutes they begin, first to leak, then to melt, and finally to disintegrate. So, Gog-Agog is regularly distracted by putting her face back on.

3) Despite being an eldritch abomination that is also chaotic evil -- /very/ chaotic, and /very/ evil -- Gog-Agog can appear to be perfectly friendly. In fact, she can be downright chipper -- cheerful, perky, and filled with childlike enthusiasm and fun. This is an eldritch abomination that introduces itself as "Your pal, Gog-Agog!" Inside, she's a profoundly alien intelligence and also a festering mass of millenia-old resentments. She's known as the Devourer of Worlds, and there's probably a good reason for that. But she is also super easily distracted. She likes things that are cool! Basically she's a horrifically powerful pseudo-Lovecraftian nightmare thing with bad ADHD.

Apropos of nothing except that I'd really like to adapt her into a campaign someday.

D20PFSRD has a CR14 worm that walks 13th level Conjurer... could be used as a guideline/starting point. Just as easily just add the template to whatever class and build you think fits her best.

As for the explosion of worms thing, which is awesome, you can look towards the Sentinel Prestige Class for Trelmarixian, Horseman of Famine, for inspiration... it gives you this as its third boon:

Eruptive Arrival (Sp) Once per day, you can teleport yourself into the flesh of any living creature that you can see (as per greater teleport), erupting out of its body in a shower of blood, bone, and viscera, arriving in an adjacent square, and dealing 5d6 damage to all creatures within 10 feet. The target itself takes 20d6 points damage. The target and creatures in the affected areas can attempt Fortitude saves (DC = 10 + half your Hit Dice + your Constitution bonus) to reduce the damage by half, but any creature that fails this saving throw is also nauseated for 1d4 rounds.

Definitely don't have to make her take the Prestige Class, but you can steal that ability if she is a BBEG, devourer of worlds.

If enough people sign up to be infected the chance that each person's number comes up should be fairly low. I can see people taking on that risk for enough money or opportunities. Or out of fear of the consequences of saying no - 'willing' doesn't have to mean they like the idea.

You seem to have more detail on Gog-Agog than is in the story. Where does that come from?

In the webcomic, she's had her head blown off at least three times. It appears to annoy her without doing any actual damage. So, AC doesn't seem to be an issue. In PF terms, we might model that as either crazy high DR, or crazy fast regeneration.

It's packed full of amazing little details that require a couple of rereads to catch. Like, in the dream sequence with Incubus in his "office", he has a mug on his desk saying "World's Greatest GOD" and his secretary is just himself in drag. Also, the drinking contest that results in the creation of Princess is one of the best webcomic sequences anywhere ever.

"Hey! Try it out yourself! Eat this worm! If you eat it, you'll become me! And being me is reaaaaally fun!"

So additional data from the latest page of the webcomic: you can choose to allow Gog-Agog into you, and if you do, you gain some benefit. "Everyone wants to feel pretty... satisfied.. happy!" In PF terms, perhaps you gain +4 Cha, along with a nebulous but real sense of confidence and well-being. Of course the drawback is that Gog-Agog can now see through your eyes; can take over your body at any time; and can manifest herself wherever you are, killing you quickly and horribly in the process.

If you want to make her more of a boss than a demigod, you could say that (1) the number of worm-hosts she can have at one time is limited to her Cha bonus, and (2) otherwise it works like Eruptive Arrival, described above. In this case, yeah, I think you can pretty much just model her as a Worm that Walks with maybe an additional +1 CR.